A retired Met police officer may just have captured the mood of many Scottish voters. With the precise but soft cadence of a Hebridean islander, Douglas MacKenzie had one prediction to make about the outcome of this Thursday's Scottish parliament election.

The Liberal Democrats, he said, would experience a "terrible backlash" on election day. Too many voters found it difficult to accept or forgive the party's coalition with the Tories in London. "They just grabbed for power," he said. "I think they deserve a terrible backlash. Traditionally, they're not Tories, they're the absolute opposite and I think people were very disappointed."

Standing on the high street in the Highland market town of Grantown on Spey, MacKenzie had just met one of the Scottish Lib Dems most closely identified with the coalition - Danny Alexander, its youthful Treasury minister, the local MP and the Lib Dem insider who brokered Nick Clegg's mould-breaking, power-sharing deal with David Cameron.

Alexander's local popularity appeared far greater than MacKenzie's caustic assessment. Locals approached the chief secretary to the Treasury with ready smiles, arms stretched out for a handshake. He even appeared to convert one Tesco employee, Jean Irvine, after a brief conversation about the need for deep spending cuts. "The thing is, some unpopular things have to be done. It's a sad fact. You're not going to please everyone all the time," she said. "I certainly know that," he replied.

Yet the polls appear to agree with MacKenzie and suggest a very different fate for the Scottish Lib Dems on Thursday. Their fate will play a large part in settling the question of who governs the devolved parliament in Edinburgh for the next five years. In turn, that is likely to have a substantial bearing on the future of the UK.

Ominously for the Labour party and its leader Ed Miliband, the latest opinion poll results are unanimous: Alex Salmond is poised to win a second term as first minister, allowing him five more years to consolidate the nationalists in power. The most recent polls on Sunday put the Scottish National party comfortably ahead, by up to 10 points according to one survey.

One of the main factors in the SNP's lead in the polls has been the apparent shift by tens of thousands of former Liberal Democrat voters towards the nationalists - a switch which has caught Labour and its Scottish leader, Iain Gray, by surprise, and delighted Salmond.

The polls repeatedly show that Lib Dem support has halved, to about 8%, leaving it with perhaps fewer than 10 seats come polling day, while the SNP's support has soared. If these polls are reflected accurately on Thursday, Salmond and the SNP will be returned for a second term with well over 50 seats in Holyrood; not enough for an overall majority of the 129-seat parliament but enough to dominate.

Enough, perhaps, to force the few remaining Lib Dems at Holyrood to agree to support a referendum on Scottish independence in three or four years' time, in exchange for direct influence on an SNP government's policies. It now seems that in large areas of Scotland - from the southern Highlands of Perthshire to Cape Wrath in the far north and the oil capital of Aberdeen to the east - the political map of Scotland could turn SNP yellow on 5 May.

At an earlier stage in the campaign, Gray's strategists believed Labour would be the natural home for disaffected Lib Dem voters. They now admit they were mistaken. Two months ago, Labour was 10 points ahead. But last Thursday Miliband, speaking at a town hall-style event in the coastal town of Portobello in eastern Edinburgh, implied that Labour faced defeat. "Remember [George] Bush versus [Al] Gore in 2000 in the United States? That election came down to a few hundred votes in Florida," he said. "This election could come down to that; the stakes are that high."

The polls have pushed Labour into fighting a very different election campaign. Its manifesto pledges on ending youth unemployment are now overshadowed. So too are Labour's "dog whistle" attacks on the Tories in London, and its attempts to resurrect the ghosts of Margaret Thatcher.

Last week, Salmond said a second term in office would be a "mandate" to hold a vote on independence. So Gray has focused instead on threatening the large number of undecided voters - one poll suggested a third of voters had yet to choose a party - with alarmist warnings about the apparent threat Salmond poses to the future of the UK.

As he prepared for another televised leaders' debate on Sunday night, Gray claimed Scotland would face a £13.75bn "black hole" in its finances if it became independent, costing every Scot £2,600 each. The SNP dismissed these figures as "complete garbage" but on Monday the Lib Dems' Scottish leader, Tavish Scott, supported Labour's strategy, weighing in with his own assault on separatism. "An SNP vote is for independence and five years of a permanent political campaign for separatism," he said.

Labour sources say the shift towards the nationalists is particularly great in rural and affluent suburban areas: the traditional Highland and countryside seats that the Lib Dems in Scotland regard as their heartlands, areas represented in the Commons by former UK leader Charles Kennedy and previously by Alexander's mentor Russell Johnstone.

Some Labour officials even talk privately about the SNP taking seats off the Liberal Democrats in the Borders. This is the region that produced the Liberal leader David Steel, one where many assumed its proximity to England, its shared history and population flows, would work against the SNP.

Alexander and his Lib Dem colleagues are adamant the polls are too crude, and fail to take account of local loyalties and local politics. Outside the political bubbles of Westminster and Holyrood, voters think for themselves, Alexander said, particularly in the Highlands. "I'm just not seeing the levels of support for the SNP you're seeing in the polls. I'm just not seeing it," he said.

At one point in Grantown on Spey, as they delivered leaflets on a prosperous side street of detached houses and manicured lawns, a car drew up beside Christine Jardine, the local Lib Dem candidate. Its driver, Susan, a former policewoman, leant over her daughter in the passenger seat to pledge her support to Jardine.

Susan had been captured by the Lib Dems' promise to oppose SNP proposals to create one Scottish police force, abolishing eight local forces. It is an emblematic issue. "I can't stand the way everything is being centralised at the moment. The SNP is supposed to be for the whole of Scotland, but everything seems to be going towards the central belt," she said.

Yet Labour's attempts to turn this campaign into a battle about the future of the UK appear to have failed. While it showed Labour was closing the gap on the SNP, a YouGov survey for the Scotsman on Monday suggested that 50% of Scots believe the SNP would do a better job of standing up for Scotland against the coalition in London than Labour: only 31% believe Gray can best combat Cameron.

Scots appear uninterested about a future referendum on independence. YouGov continues to show support for independence hovering around 30%, even as half of Scottish voters appear to prefer Salmond as first minister. On Thursday, Gray has promised that 10,000 Labour activists - a group the party has dubbed Labour's Volunteer Army - will be out galvanising and chauffeuring its voters to the polling stations to prove the polls wrong; to do what Gore failed to do in 2000.

Meanwhile the party's candidates are preparing themselves for defeat. Dissenting voices about Labour's campaign are already beginning to surface. One candidate whose hopes of unseating a sitting SNP minister are now disappearing, began hinting as much but stopped himself short. "This conversation will have to stop, but it isn't finished," he said.